Two-stage process for preparation of polyphenylene oxides

ABSTRACT

Polyphenylene oxides are prepared by the catalytic reaction of oxygen with a monohydroxyaromatic compound such as 2,6-xylenol in a solvent for reactants and product, in a two-stage process. The first stage is effected continuously in at least one and preferably not more than two back-mixed (e.g., tank) reactors, and the second stage in one or more batch reactors or, preferably, in a reaction system with limited back-mixing, typically a cylindrical reactor containing multiple agitated zones. In the case of a copper catalyst system, it is also preferred to pre-mix the non-gaseous constituents of the reaction mixture in an inert atmosphere.

This application is a continuation-in-part of copending application Ser.No. 659,045, filed Oct. 9, 1984, now abandoned which in turn is acontinuation-in-part of application Ser. No. 479,066, filed Mar. 25,1983, now U.S. Pat. No. 4,477,649, and Ser. No. 609,075, filed May 10,1984, now abandoned. The disclosures of all of said applications areincorporated by reference herein.

This invention relates to the preparation of polyphenylene oxides, andmore particularly to a two-stage oxidative coupling process for suchpreparation which is adaptable to continuous operation.

For the most part, the present processes for the preparation ofpolyphenylene oxides (also known as polyphenylene ethers) are batchprocesses. Reference is made, for example, to the following U.S.patents:

U.S. Pat. No. 3,306,875 (hereinafter '875)

U.S. Pat. No. 3,914,266 (hereinafter '266)

U.S. Pat. No. 4,028,341 (hereinafter '341).

A problem associated with batch operation is variation from batch tobatch in product quality. In addition, continuous processes frequentlyoffer lower capital and operating costs per unit of production thanbatch processes, especially in large-scale production.

There have been disclosed various processes possibly adaptable tocontinuous production of polyphenylene oxides. For example, U.S. Pat.No. 3,306,874 (hereinafter '874) and Japanese Kokai No. 80/21798(published application No. 80/40613) disclose polymerization processesusing three reactors in series. A similar process using two reactors isdisclosed in Japanese Kokai No. 73/45600. Three different kinds ofcolumn reactors are disclosed in Japanese Kokai No. 74/08597, JapaneseKokai No. 80/55996 and Czechoslovakian Patent No. 192,278. Thesereaction systems suffer from various disadvantages including arelatively high catalyst level and an unduly long residence time in oneor more reactors.

A principal object of the present invention, therefore, is to provide animproved process for the preparation of polyphenylene oxides.

A further object is to provide such a process which is convenientlyadapted to continuous production on a commercial scale.

Still another object is to provide such a process which, when operatedcontinuously, affords improvements over previously disclosed continuousprocesses, including lower catalyst level and lower overall residencetime in the reaction system.

Other objects will in part be obvious and will in part appearhereinafter.

In its broadest sense, the present invention is an improvement in anoxidative coupling process for preparing polyphenylene oxides by thecatalytic reaction of oxygen with at least one monohydroxyaromaticcompound in solution in a solvent in which said polyphenylene oxide isalso soluble, said improvement comprising carrying out said reaction intwo stages, the first stage being conducted continuously in at least oneback-mixed reactor and the second stage in at least one batch reactor orcontinuously in a reaction system with limited back-mixing.

The invention, while not limited to any particular theory, is based on anumber of discoveries about the nature of the oxidative couplingreaction leading to the polyphenylene oxide. In the first place, saidreaction in its early stages (i.e., up to about 90% conversion) isessentially zero order; that is, its rate is essentially independent ofreactant concentration. Moreover, in early stages a high concentrationof monohydroxyaromatic compound can promote formation of by-productssuch as tetramethyldiphenoquinone. In later stages, however, thereaction is first order with respect to concentration of the hydroxygroup. At that point, of course, said concentration is relatively low,since a large proportion of the available hydroxy groups have beenconverted to ether groups. Therefore, the reaction is quite slow inthese later stages.

In the second place, the oxidative coupling polymerization isessentially an equilibrium reaction. Therefore, if both high molecularweight and low molecular weight polymer are present a leveling effectoccurs and the resulting mixture assumes an intermediate molecularweight. It is therefore desirable to segregate monohydroxyaromaticreactant and low molecular weight polymer from high molecular weightproduct. Under such conditions, the reaction kinetics provide a highmolecular weight product with the use of less catalyst, a lowerresidence time and less oxygen.

The invention takes advantage of these conditions by conducting thefirst stage of the reaction in one or more back-mixed reactors, whereinpolymerization is relatively rapid and as a result themonohydroxyaromatic compound concentration is low enough to minimizeby-product formation. The second stage is conducted in a system whichsegregates higher molecular weight product, in which hydroxy groupconcentration is low, from the lower molecular weight material in whichit is higher. This segregation may be spacewise as in a continuouslimited back-mixing reactor, or timewise as in one or more batchreactors. The result is an increase in the overall rate ofpolymerization, both because of the first-order nature of the reactionand because it is an equilibrium reaction.

Typical monohydroxyaromatic compounds (hereinafter sometimes referred toas "phenols" for brevity) useful in the process of this invention arethose having the formula ##STR1## where R¹ is a lower primary alkylgroup and R² is a lower primary or secondary alkyl group, the word"lower" meaning that it contains up to 7 carbon atoms. Examples of lowerprimary alkyl groups are methyl, ethyl, n-propyl, n-butyl, isobutyl,n-amyl, isoamyl, 2-methylbutyl, n-hexyl, 2,3-dimethylbutyl, 2-, 3- or4-methylpentyl and the corresponding heptyl groups. Examples of lowersecondary alkyl groups are isopropyl, sec-butyl and 3-pentyl.Preferably, R¹ and R² are straight chain rather than branched. Since thepolyphenylene oxides in which R¹ and R² are other than methyl generallyhave no more desirable properties than those in which R¹ and R² are bothmethyl, and since 2,6-xylenol is the most readily available and cheapest2,6-dialkylphenol, its use is preferred. The polyphenylene oxideobtained is then poly(2,6-dimethyl-1,4-phenylene oxide). Other suitablephenols are disclosed in the '874, '875 and '341 patents, thedisclosures of which are incorporated by reference herein.

Various catalyst systems have been disclosed for the preparation ofpolyphenylene oxides, and any of them can be used in the process of thisinvention. For the most part, they contain at least one heavy metalcompound such as a copper, manganese or cobalt compound, usually incombination with various other materials.

A first class of preferred catalyst systems consist of those containingcopper. They are usually combinations of cuprous or cupric ions, halide(i.e., chloride, bromide or iodide) ions and at least one amine.

The source of copper can be any of the cupric or cuprous salts disclosedin the '874 and '875 patents. See, for example, '874 from column 3, line62, to column 4, line 61. The halide ion is preferably bromide, and itssource can be any of those disclosed in the '341 patent; particularreference is made to column 8, line 61, to column 9, line 53. Forexample, it can be an inorganic bromide (except for ammonium bromide,because the ammonium ion can also form a strong complex with copperions) and can include bromine and hydrogen bromide. Also useful areorganic bromine compounds which, under reaction conditions, producebromide ions. An example thereof is 4-bromo-2,6-xylenol. The only basicrequirement is that the bromine compound be capable of supplying a formof bromide ion which is soluble in the reaction mixture. If the brominecompound itself is insoluble, it can still be satisfactory if it formssoluble complexes with the amine constituents of the catalyst orproduces a soluble product under oxidative coupling conditions. Whenmetal bromides other than the copper bromides are used, the particularmetal used is merely one of choice. Since some of these materials (e.g.,cobalt) form complexes with amines, suitable adjustments in the amountof amine used may sometimes be necessary. Because of low cost and readyavailability, when using a metal bromide often the alkali or alkalineearth metal bromides are used, e.g., sodium bromide. Since hydrogenbromide will react with amines to form an amine hydrobromide salt andbromine will brominate the phenol and simultaneously produce hydrogenbromide, again adjustments in the amount of amine may be necessary insuch situations.

The currently preferred bromide source is HBr, which may conveniently becombined with the copper source as a solution of cuprous oxide inaqueous hydrobromic acid.

The amine constituents of the copper catalyst system may be any of thosedisclosed in the '874, '875, '266 and '341 patents. Preferably, however,the amines comprise at least one secondary alkylene diamine and at leastone tertiary monoamine.

The secondary alkylene diamine may be selected from those disclosed inthe '341 patent, especially from column 6, line 44, to column 8, line11. It generally has the formula

    R.sup.3 NH--R.sup.4 --NHR.sup.5

wherein each of R³ and R⁵ is a secondary or tertiary alkyl group and R⁴is a divalent hydrocarbon group, and wherein at least two and no morethan three carbon atoms separate the two amino nitrogen atoms and thecarbon atoms to which the amino nitrogens are attached are aliphatic.Preferably, there are only two carbon atoms separating the two aminonitrogens. The two or three carbon atoms separating the amino nitrogenscan be either acyclic or cyclic carbon atoms. Typical examples of R⁴include ethylene, 1,2- and 1,3-propylene, 1,2-, 1,3- and 2,3-butylene,the various pentylene isomers having from two or three carbon atomsseparating the two free valences, phenylethylene, tolylethylene,2-phenyl-1,2-propylene, cyclohexylethylene, 1,2- or 1,3-cyclohexylene,1,2-cyclopropylene, 1,2-cyclobutylene and 1,2-cyclopentylene.

Typical examples of R³ and R⁵ include isopropyl and tertiary alkyl(e.g., t-butyl) groups. The substituents on the α-carbon atoms can bestraight or branched chain alkyl, cycloalkyl, aryl or alkaryl. Otherexamples include those set forth in the '341 patent, column 8, lines2-11, e.g., 2-methyl-2-butyl, etc. The currently preferred secondaryalkylene diamine is N,N'-di-t-butylethylenediamine.

The tertiary monoamine can be selected from those disclosed in the '341patent; specific reference should be made to column 8, lines 12-33. Itcan be a heterocyclic amine or a trialkylamine characterized by havingthe amine nitrogen attached to at least two groups which have a smallcross-sectional area. In the case of a trialkylamine, it is preferredthat at least two of the alkyl groups be methyl with the third being aC₁₋₈ primary or C₃₋₈ secondary alkyl, and it is more preferred that thethird substituent have no more than four carbon atoms. The currentlypreferred tertiary monoamine is dimethyl-n-butylamine.

At least one secondary monoamine as disclosed in the '874 patent fromcolumn 4, line 62 to column 6, line 13 may optionally also be used. Inaddition to functioning as part of the catalyst and increasing theactivity thereof, the secondary amine frequently becomes chemicallybonded to the polymer, at least in part, and increases the impactstrength thereof, particularly in blends with other polymers such aspolystyrenes. It is believed that the increase in impact is achieved bya crosslinking reaction similar to that disclosed in U.S. Pat. No.4,054,553 at column 6, lines 28-60. The currently preferred secondarymonoamines are dimethylamine and di-n-butylamine. The use ofdimethylamine for this purpose in polyphenylene oxide preparation isdisclosed and claimed in copending, commonly assigned application Ser.No. 501,477, filed June 6, 1983.

It is within the scope of the invention to use copper catalyst systemscontaining complex salts such ascopper(I)-(N,N-di-t-butylethylenediamine) 2,6-xylenoxide, as disclosedand claimed in copending, commonly assigned application Ser. No.572,036, filed Jan. 19, 1984.

Manganese-containing systems constitute a second preferred class ofcatalysts. They are generally alkaline systems containing divalentmanganese and such anions as halide, alkoxide or phenoxide. Most often,the manganese is present as a complex with one or more complexing and/orchelating agents such as dialkylamines, alkanolamines, alkylenediamines,o-hydroxy aromatic aldehydes, o-hydroxyazo compounds, ω-hydroxyoximes(monomeric and polymeric), o-hydroxyaryl oximes and β-diketones. As inthe copper-containing systems, secondary amines such as dialkylaminesfrequently become chemically bound to the polyphenylene oxide productand increase its impact strength.

The following patents are incorporated by reference herein for theirdisclosures of manganese-containing catalyst systems:

    ______________________________________                                        3,956,242      4,075,174                                                                              4,110,312                                             3,962,181      4,083,828                                                                              4,184,034                                             3,965,069      4,093,596                                                                              4,315,086                                             3,972,851      4,093,597                                                                              4,335,233                                             4,054,553      4,093,598                                                                               4,385,168.                                           4,058,504      4,102,865                                                      ______________________________________                                    

Also useful in the method of this invention are cobalt-containingcatalyst systems such as those disclosed in U.S. Pat. Nos. 3,455,880 and4,058,504, the disclosures of which are also incorporated by referenceherein.

A phase transfer catalyst may optionally be used in the reaction systemas a reaction rate promoter. Useful phase transfer catalysts aredisclosed in U.S. Pat. No. 3,988,297, hereby incorporated by reference;specific reference is made to column 2, lines 11-26, and column 3, lines1-23. The currently preferred phase transfer catalyst (especially forcopper-containing systems) is Adogen 464, which is amethyltrialkylammonium chloride wherein the alkyl groups have from 8 to10 carbon atoms.

The presence of one or more solvents for reactants, catalyst andpolyphenylene oxide product is an essential feature of the invention.Typical solvents for copper-containing systems are disclosed in the'874, '875 and '341 patents. Illustrative solvents for this purpose aretoluene and benzene; other inexpensive and readily available commercialsolvents may also be used. For manganese systems, solvents of the sametype may be used in combination with minor amounts (usually about 5-10%by weight) of lower alkanols (preferably methanol) or the like whichmaintain the manganese compounds in solution.

According to the present invention, the oxidative coupling reactionproducing the polyphenylene oxide is carried out in two stages. Thefirst stage is effected continuously in at least one back-mixed reactor.Back-mixed reactors include tank and certain types of loop reactors.Particularly preferred are continuous-flow stirred tank reactors(hereinafter "CSTR's"), which are known to be back-mixed reactors;reference is made to Perry, Chemical Engineers' Handbook, FourthEdition, p. 19-11 (FIG. 19-22), and Levenspiel, Chemical ReactionEngineering, Second Edition, p. 98 (FIG. 1c). Because of thispreference, CSTR's are frequently referred to hereinafter, but it shouldbe understood that other back-mixed reactors may be substituted thereforwhen appropriate. It is also within the scope of the invention to usetwo CSTR's in series, but the use of more than two offers little or noadvantage. Reference hereinafter simply to a "CSTR" will denote thefirst or only such vessel, with "second CSTR" denoting the optionalsecond such vessel.

Reaction is initiated in the CSTR with oxygen being sparged into thesame and sufficient agitation being provided to ensure efficientgas-liquid contact. Any suitable agitation means can be used, e.g., aflat-bladed turbine agitator. The object at the beginning of a run is toachieve steady state conditions as soon as possible. This may beaccomplished by means known in the art. For example, the reaction may berun batchwise until a high conversion level is reached and thencontinuously.

The heat of reaction is usually removed from the CSTR to maintain aconstant temperature in the range of about 10°-60° C., usually 20°-55°C. and preferably 30°-35° C. This can be accomplished in conventionalmanner, e.g., reaction solution can be circulated from the CSTR throughexternal heat exchangers where heat is removed by a cooling fluid, orcooling coils internal to the CSTR or an external cooling jacket can beused. The outlet stream from the CSTR is fed either to a second CSTR orto the second stage reactor(s).

The residence time in the CSTR will generally be from about ten minutesto two hours, preferably 20-60 minutes and most preferably about 30minutes.

The pressure in the CSTR is typically atmospheric with oxygen beingsparged thereinto at one atmosphere. If desired, the oxygen can bediluted with inert gases or air can be used, but the use of pure oxygenis preferred. Subor superatmospheric pressures can be used but areseldom if ever necessary.

The amount of oxygen is generally at least the stoichiometric amountneeded to react with the phenol to achieve the desired level ofconversion. Amounts substantially in excess of stoichiometric can beused, of course; for example, at a 70% molar excess of oxygen theinterfacial area between the gas and liquid phase is increased. However,it is generally found that if high agitation is used so much oxygen isnot required; e.g., at 10% molar excess of oxygen the reaction readilyproceeds to the desired degree of conversion.

Usually, at least about 65% of the hydroxyl groups in the phenol areconverted to ether linkages in the CSTR, most desirably about 90%conversion being achieved. At conversions much less than about 65%, anincreased conversion level will be required in the later stages of theprocess; this is not desirable because it is then difficult to attainhigher molecular weights.

Because of the nature of the polymerization, a large proportion of thetotal conversion, and thus a large proportion of the total heat release,can take place in the CSTR without forming polymer of high molecularweight. Thus, per the process of the present invention the majority ofheat release takes place under a condition which is conducive toefficient heat transfer, i.e., low solution viscosity, typically on theorder of less than about 10 cps. Of course, as the percent conversionincreases, viscosity increases because of the increasing molecularweight of the polymers formed in the system. If necessary at this orother points in the process, additional solvent may be added to decreasesolution viscosity.

After the desired degree of conversion is reached, water may be removedfrom the reaction mixture by centrifugation, decantation or equivalentmeans. Water removal is optional but may be desirable, since water maycause partial catalyst deactivation. The mixture then passes either to asecond CSTR or to the limited back-mixing reactor.

The pressure of operation, temperature of operation and degree ofagitation in the second CSTR (if used) are essentially the same as thoseused in the first CSTR. Somewhat less oxygen is necessary, however,since the conversion therein is lower than the first CSTR. The residencetime in the second CSTR is typically about 20-90 minutes, preferably30-50 minutes and most preferably about 30 minutes. Water removal afterthe second CSTR is also an optional but frequently preferred step.

In the first CSTR, the primary effect desired is to achieve a highpercentage of the total conversion; in the second stage reaction system,it is to increase molecular weight. In the second CSTR, when used, anintermediate effect is achieved, i.e., increasing percent conversion,though not as much as in the first CSTR, and increasing molecularweight, though not as much as in the second stage reaction system.

While cooling is generally necessary in the first CSTR because of thehigh percent conversion, as consequence of lower percent conversions isthe second CSTR, heat removal may not be necessary in some instances.Solution viscosity does somewhat increase in the second CSTR, but thesolution has a relatively low viscosity, in most instances probably nomore than about 20 cps.

The conversion level of the product is typically increased no more thanabout 5-30% in the second CSTR. However, since there is a relativelyhigh percent conversion in the first CSTR, in the second CSTR one canessentially increase weight average molecular weight in the productseveralfold, typically at least fivefold.

The second stage of the process of this invention is effected either inat least one batch reactor or continuously in a reaction system withlimited back-mixing; that is, one which approaches plug flow. The term"plug flow" is defined in Levenspiel, op. cit., p. 97, as follows:

It is characterized by the fact that the flow of fluid through thereactor is orderly with no element of fluid overtaking or mixing withany other element ahead or behind. Actually, there may be lateral mixingof fluid in a plug flow reactor; however, there must be no mixing ordiffusion along the flow path.

Thus, "limited back-mixing" in the present context means that there islittle or, ideally, no mixing of high molecular weight with lowermolecular weight polyphenylene oxide. Limited back-mixing reactionsystems are typified by continuous-flow tubular reactors, especiallythose in which baffles, packing, multiple reaction zones or the like arepresent to minimize flow in the reverse direction.

At first glance, it may appear that there is little or no similaritybetween the two kinds of second stage reactors which may be employed.Those skilled in the art will, however, recognize the similaritiesbetween batch reactors and limited back-mixing continuous reactors. Aspecific element of fluid is ideally homogeneous in either type ofreactor with respect to degree of completion of the reaction. In a batchreactor, said element is the entire contents of the reactor and theprogress of the reaction is orderly in relation to time. In a limitedback-mixing reactor, each element passing through is in an orderly stateof progress in relation to space. The overall result is the sameirrespective of which reaction system is used.

When batch reactors are employed in the second stage, it may beadvisable to interrupt the polymerization reaction until an entire batchhas been charged to a reactor. This may be done by interrupting oxygenflow or, when necessary, by introducing an inert gas such as nitrogen.It is preferred to keep the interruption time as short as possible inorder to maintain maximum catalyst activity, particularly when amanganese catalyst system is employed.

In a batch reactor system it is generally preferred to use a pluralityof such reactors, charging the feed from the CSTR thereto in successionfor maximum efficiency. It is also within the scope of the invention toutilize the CSTR as a batch reactor at some point by shutting off itsfeed and outlet streams.

Preferably, the second stage reaction system consists of a limitedback-mixing reactor. A typical reactor of this type is divided intomultiple reaction zones by horizontal baffles which restrict the flow offluid from one stage to a preceding zone. Such a reactor is frequentlyreferred to hereinafter as a "multi-zone reactor". One skilled in theart will recognize that the degree of back-mixing in such a reactor canbe controlled by such design variables as the number of zones and thecross-sectional area of the horizontal baffles with respect to thecross-sectional area of the column. Typically the multi-zone reactor isan upright cylindrical vessel. Oxygen is sparged into the multi-zonereactor and each stage is agitated to provide efficient gas-liquidmixing, typically by turbine agitators. However, other agitation methodscan be used such as reciprocating plate agitators and the like. Whileco-current flow of liquid feed stream and oxygen is typically employed,countercurrent flow is also possible.

The number of zones in the multi-zone reactor will obviously be greaterthan one, since one stage would be equivalent to a CSTR. As one skilledin the art will appreciate, more zones provide more limited back-mixing.It is currently believed that at least two zones will be necessary toachieve any significant limitation of back-mixing, and at least fivezones are preferred. The number of zones will generally be set byprocess economics since increasing the number of zones will increase thecost of the reactor. Practically speaking, a reactor with more than 50zones is unlikely, and usually about 5-20 zones are acceptable.

It is also possible to use, in place of a multi-zone reactor, any ofvarious other reactors which provide limited back-mixing. For example, atubular reactor containing static mixer elements can be used. Anotheralternative is a multi-tray gas-liquid contactor, which has essentiallythe same design as a sieve-tray distillation column. Still another is apacked bed reactor, which promotes a high gas-liquid interfacial areaand a good dispersion of the gas and liquid phases without the necessityfor introduction of energy to effect agitation. Other types of limitedback-mixing reactors will be apparent to those skilled in the art.

As earlier indicated, the main effect desired in the second stagereaction system is to increase molecular weight; for example, thereaction solution entering said system may have a weight averagemolecular weight on the order of less than 5000, which may be increasedtherein to 75,000 or more. Conversion, is, of course, substantially lessthan in the CSTR's. Typically a 50,000 weight average molecular weightwill be obtained at greater than 99 percent conversion.

In a manner similar to the CSTR's, agitation is provided in the secondstage reaction system so as to ensure good gas-liquid contact betweenthe reaction solution and oxygen being sparged therein. The oxygen flowrate is at least stoichiometric for the conversion, and is generally atleast two times stoichiometric to assist in increasing the gas-liquidinterfacial area. It does not appear that a flow rate as high as fivetimes stoichiometric substantially assists the reaction and, as will beapparent to one skilled in the art, the use of too high a flow ratecould lead to stripping of solvent or liquid catalyst ingredients and,of course, wasting oxygen.

The pressure in the second stage reaction system is essentially the sameas in the CSTR's, i.e., essentially atmospheric, but sub- andsuperatmospheric pressures are not excluded.

The temperature is typically on the order of about 20°-60° C.,preferably 30°-40° C. Cooling and heating of the reactor(s) can beaccomplished in the manner as discussed for the CSTR's, i.e., externaljackets, internal coils, etc. It is also possible to cool and/or heatvarious zones differently. For example, it may sometimes be advantageousto cool the initial zones of a multi-zone reactor to remove heat ofreaction while heating later zones to decrease solution viscosity.

The average liquid residence time in the second stage reaction system isabout 5-90 minutes, preferably 10-40 minutes. Exceedingly low residencetimes are insufficient for the desired increase in molecular weight, andat exceedingly high residence times catalyst deactivation isencountered.

When a copper catalyst system is employed, it is frequently preferred topre-mix the non-gaseous constituents (i.e., phenol, components of thecatalyst, solvent and phase transfer catalyst when used) in an inert(e.g., nitrogen or helium) atmosphere to form a homogeneous mixturewhich is fed to the first stage. This pre-mixing step in its moregeneral application is disclosed and claimed in copending, commonlyassigned application Ser. No. 479,057, filed Mar. 25, 1983. It isbelieved that the ingredients of the copper catalyst system interactwith each other more efficiently in the absence of oxidant (i.e.,oxygen) and in the presence of a high concentration of phenol, resultingin higher conversion and a decrease in amount of catalyst required whena pre-mixing stage in an inert atmosphere is employed. Thus, such astage promotes formation of the actual catalyst species under extremelyfavorable conditions. Inert pre-mixing is generally neither required norsuitable when a manganese catalyst system is employed, since maximumcatalyst activity in such systems is attained by adding the manganesereagent to a phenol-oxygen mixture and maintaining it in continuouscontact with oxygen to the extent possible.

Pre-mixing may be effected in a batch or continuous operation. When itis a batch operation, the copper and halide ions should be added last inorder that they will be solubilized by complex formation with theamines. It is within the scope of the invention to pre-mix and store alarge catalyst batch, using it as required in the polymerizationprocess.

Continuous pre-mixing operations may be conducted by in-line blending(i.e., with no pre-mixing vessel) or may utilize a vessel for thepre-mix step. In the former case, the order of mixing should be aspreviously described. In the latter, no special addition order isnecessary since each catalyst ingredient is always present in saidvessel. Under these conditions, a catalyst species is formed which ishighly active under oxidative coupling conditions and which retains highactivity for a relatively long period of time, thus continuing topromote effective polymerization for the duration of the polymerizationprocess.

The polyphenylene oxides produced by the process of this inventiontypically have weight average molecular weights of about 5,000 to75,000, corresponding to intrinsic viscosities of about 0.1-0.75 dl./g.as determined in chloroform at 25° C. The molecular weight is preferablyabove about 50,000. The percent product in the final reaction solutionis obviously determined by the amount of phenol introduced, sinceessentially all of said phenol is converted to polymer per the presentinvention. The product polymer may be isolated from solution byconventional methods such as precipitation by addition of a non-solventfor the polymer.

One unique benefit of the process of the present invention is its highflexibility with respect to the use of various proportions of materials,enabling one to prepare polyphenylene oxides of varying molecularweights with flexibility. However, as with all processes, there arecertain preferred proportions which are now discussed.

The phenol is generally used in an amount of about 5-60% of totalsolution weight, preferably 10-40% and most preferably 15-25%. Productswhich have a commercially desirable molecular weight are most easilyobtained in the area of 20% phenol.

Metal (e.g., copper or manganese) ratios are generally 1 mole of metalto about 100-1500 and preferably 250-1000 moles of phenol. In the caseof a copper system, the molar ratio of halide (preferably bromide) tocopper ions in the catalyst affects catalyst activity, and a ratio of atleast about 3.5 moles halide to 1 mole copper is preferred. The upperlimit of this ratio is not critical and molar ratios as high as 6 or 12or more can be used. Currently preferred molar ratios are 4-6 moles Brper mole Cu. The secondary alkylene diamine is generally used in anamount of about 0.4-3 moles, and the tertiary monoamine in an amount ofabout 10-100 moles and preferablv 20-60 moles, per mole of copper.

The molar ratio of phenol to alkali (usually sodium hydroxide orpotassium hydroxide) in a manganese system is usually about 5-40:1. Itis most often about 10-20:1, and preferably about 14-18:1 when thephenol is 2,6-xylenol.

The secondary monoamine, when present, is generally used in an amount upto 3 mole percent based on phenol, with 0.5-2 mole percent beingpreferred. The phase transfer agent, when present, is typically used inan amount of up to 0.8%, preferably 0.1-0.2%, by weight based on phenol.

It is within the scope of the invention to introduce all of each reagentat the beginning of the system, or to introduce various reagentsincrementally at various points in the system. For example, when apre-mixing stage is employed the entire amount of phenol may beintroduced into said pre-mixing stage, or a portion thereof (typicallyabout 20-50% of the total amount) may be added at a later stage, mostoften into the first reaction vessel. The same is true of the catalystingredients, although replenishment of copper catalyst in major amountat a later stage is not as important when a pre-mixing stage is presentas when it is absent. The catalyst ingredients most usually addedincrementally are copper, bromide and secondary alkylene diamine. Ifincremental addition is employed, the following weight percentageamounts of these reagents are typically added in later stages:

Copper--5-25%, preferably 20-25%

Bromide--10-30%, preferably 25-30%

Diamine--20-50%, preferably 30-50%.

Per the process of the present invention the molecular weight of thepolyphenylene oxide obtained can be controlled in simple fashion, withthe primary process parameters which affect molecular weight being theratio of catalyst to phenol, the percent monomer in the solution, thetemperature and residence time in the reactors. The degree of agitationin the reactors and oxygen introduction rates are generally secondaryparameters.

Reference is now made to the drawings in which

FIG. I is a schematic diagram of a continuous multi-zone limitedback-mixing reactor useful in the second stage of the process of thisinvention,

FIG. II is a cross-sectional view of one stage of said reactor along theline II--II of FIG. I, and

FIG. III is a schematic diagram of a typical apparatus for carrying outthe entire process of the invention.

Reactor 1 as shown in FIG. I has ten zones, one of which is designatedas 2 and shown in cross-section in FIG. II. Oxygen is sparged via line3, reaction solution is introduced via line 4 and product is withdrawnvia line 5. Centered in each zone is a turbine agitator 6; all suchagitators are driven by motor 7 via shaft 8. Each zone is provided withfour equally spaced vertical baffles 9 and with a horizontal baffle 10,the latter comprising an outer section 11 attached to the inner wall ofreaction 1 and an inner section 12 attached to shaft 8. Between them,outer section 11 and inner section 12 define an annular area 13 oflimited back-mixing. Usually, annular area 13 comprises about 2-15%,most often about 4-8%, of the inner cross-sectional area of reactor 1.

In FIG. III, numeral 14 is the preferred copper catalyst pre-mix vessel,the same being provided with agitation means 15 and a nitrogen inlet 16with feed of reaction components generally being indicated at A. Thereaction components enumerated hereinabove are thoroughly agitated incatalyst pre-mixer 14 under a nitrogen blanket or other inertatmosphere. Any conventional agitation device may be used, a flat-bladedturbine impeller being suitable. Pressure is not important, thetemperature is typically room temperature and the time of mixing is notoverly important so long as dissolution of all components is achieved.Typically, mixing may be conducted for about 15 minutes.

The feed from catalyst pre-mixer 14 is conducted via line 17 to firstCSTR 18, provided with agitation means 19 (similar to 15 ) and oxygeninlet 20. Cooling means for first CSTR 18, though not shown, willgenerally be provided. The output from first CSTR 18 is fed via line 21to second CSTR 22, which is also provided with agitation means 23(similar to 15 ) and oxygen inlet 24, as well as with cooling meanswhich are likewise not shown. Line 4 conducts the output from secondCSTR 22 to previously described multi-zone reactor 1.

The invention is illustrated by the following examples. All percentagesare by weight of total solution unless otherwise indicated, and all moleamounts are per 1000 moles of 2,6-xylenol in the original feed solution.The following abbreviations are used:

DBEDA--N,N'-di-t-butylethylenediamine

DMBA--dimethyl-n-butylamine

DBA--di-n-butylamine.

Intrinsic viscosities were measured in chloroform at 25° C.

EXAMPLE 1

The apparatus consisted of a pre-mix vessel, a single CSTR, a centrifugeand a multi-zone reactor in series. The CSTR was an upright cylindricaltank 14 inches in diameter, agitated with a 5-inch diameter turbineagitator having six blades. The tank had a 10-gallon working volume andthe agitator speed was 400 rpm. The CSTR was equipped with verticalbaffles to prevent vortexing. Conventional internal cooling coils andexternal cooling jackets were used to remove the heat of reaction. TheCSTR was maintained at 30° C. and ambient pressure with oxygen beingintroduced into the bottom thereof.

The multi-zone reactor was as shown in FIG. I. It had an internaldiameter of 3 inches, was 30 inches long and contained 10 identicalzones. With reference to FIG. II, inner section 12 had a diameter of 1.5inches and annular area 13 had a width of 0.125 inch. The diameter ofeach turbine agitator 6 was 1.5 inches; each such agitator had 6 flatblades mounted on shaft 8 and was located midway between the top andbottom of its zone. Four vertical baffles 9, each 0.25 inch wide, wereequally spaced around the circumference of the vessel. The turbines wererotated at 550 rpm. and the multi-zone reactor was operated at slightlyabove ambient pressure (typically 0-5 psig.). The multi-zone reactor wascooled or heated as necessary by means of a water jacket.

A feed solution in toluene as solvent was prepared by mixing theingredients thereof in the pre-mix vessel under nitrogen for 15 minutes.Said feed solution contained 22% 2,6-xylenol, 0.022% Adogen 464 and thefollowing proportions of other reagents:

    ______________________________________                                               Reagent                                                                              Moles                                                           ______________________________________                                               DBEDA  1.1                                                                    DMBA   44                                                                     DBA    9.4                                                                    Cu     1.7                                                                    HBr    6.9                                                             ______________________________________                                    

Copper and bromide were provided in the form of a Cu₂ O solution in 48%aqueous HBr.

The feed solution was continuously pumped into the CSTR and liquid wascontinuously withdrawn such that a constant liquid volume was maintainedand the average liquid residence time in the CSTR was 33 minutes. Oxygenwas fed into the CSTR at a rate of 60 SCFH.

The feed from the CSTR was centrifuged to remove the water of reaction.To the organic solution, under nitrogen, were added the followingadditional proportions of reagents:

    ______________________________________                                               Reagent                                                                              Moles                                                           ______________________________________                                               DBEDA  1.0                                                                    Cu     0.50                                                                   HBr    2.7                                                             ______________________________________                                    

The resulting solution was continuously fed through the multi-zonereactor at a rate such that the average liquid residence time thereinwas 20 minutes. Oxygen was fed to the multi-zone reactor at a rate of1.5 SCFH. The multi-zone reactor was maintained at an averagetemperature of 40° C. with about a ±3° C. temperature variation alongthe length of the reactor.

The polyphenylene oxide product was isolated by diluting the solutionthereof with one volume of toluene and then with approximately fivevolumes of methanol, filtering and drying in conventional manner.

EXAMPLES 2-3

The procedure of Example 1 was repeated, except that the oxygen feedrate to the multi-zone reactor was 2.0 SCFH and that different averageliquid residence times were used therein.

The residence times and the intrinsic viscosities of the polyphenyleneoxide products of Examples 1-3 are shown in the following table.

    ______________________________________                                                   Average liquid                                                                residence time                                                                            Intrinsic viscosity,                                   Example    min.        dl./g.                                                 ______________________________________                                        1          20          0.58                                                   2          10          0.14                                                   3          15          0.29                                                   ______________________________________                                    

Examples 1-3 demonstrate that polyphenylene oxides of a wide variety ofintrinsic viscosities (and thus a wide variety of molecular weights) canbe continuously produced by the process of this invention.

EXAMPLE 4

The apparatus included a second CSTR following the first and excludedthe water removal centrifuge. The second CSTR had a 16-gallon workingvolume and a 7-inch diameter turbine agitator with six blades and aspeed of 370 rpm. The feed solution was identical to that of Example 1except in the following respects:

    ______________________________________                                               Reagent                                                                              Moles                                                           ______________________________________                                               DBEDA  0.93                                                                   HBr    6.8                                                             ______________________________________                                    

The feed solution was continuously pumped into the first CSTR which wasmaintained at 32° C., and liquid was continuously withdrawn such that aconstant liquid volume was maintained and the average liquid residencetime in the first CSTR was 20 minutes. Oxygen was fed into the firstCSTR at a rate of 50 SCFH.

The product from the first CSTR was continuously pumped into the secondCSTR which was maintained at 30° C., and liquid was continuouslywithdrawn such that a constant liquid volume was maintained and theaverage liquid residence time in the second CSTR was 32 minutes. Oxygenwas fed into the second CSTR at a rate of 40 SCFH.

No attempt was made to separate water of reaction from the outletstreams from the first or second CSTR. To the outlet stream from thesecond CSTR was added, under nitrogen, 0.55 mole of DBEDA. The resultingsolution was continuously fed through the multi-zone reactor at a ratesuch that the average liquid residence time therein was 10 minutes.Oxygen was fed to the multi-zone reactor at a rate of 2.0 SCFH. Themulti-zone reactor temperature was maintained at about 36° C.±4° C.along the length of the reactor. The polyphenylene oxide product had anintrinsic viscosity of 0.51 dl./g.

EXAMPLE 5

The apparatus was identical to that of Example 1, and the feed solutiondiffered only in the presence of 6.7 moles of HBr. The temperature andaverage liquid residence time in the CSTR were 36° C. and 59 minutes,respectively. The oxygen feed rate to the CSTR was 30 SCFH. The sameproportions of ingredients as in Example 1 were added to the centrifugedproduct from the CSTR. The average liquid residence time in themulti-zone reactor was 10 minutes. The oxygen feed rate thereto was 2.0SCFH and the temperature thereof was 40° C.±3° C. The polyphenyleneoxide product had an intrinsic viscosity of greater than 0.71 dl./g.

The only significant difference between Examples 2 and 5 is thatdifferent liquid residence times in the first CSTR were used. Thisdemonstrates that polyphenylene oxides of different intrinsicviscosities can be produced by changing only the residence time in theCSTR.

EXAMPLES 6-7

These examples demonstrate that the process of this invention can beoperated at substantially different monomer concentrations and catalystto monomer ratios than shown in the previous examples. Comparisonbetween Examples 6 and 7 demonstrates that the catalyst level can beused in this process as a means of producing polyphenylene oxides ofdifferent intrinsic viscosities.

The apparatus of Example 1 was used. The feed solution contained 11%2,6-xylenol, 0.022% Adogen 464 and the following proportions of otherreagents:

    ______________________________________                                               Reagent                                                                              Moles                                                           ______________________________________                                               DBEDA  2.2                                                                    DMBA   89                                                                     DBA    19                                                                     Cu     3.3                                                                    HBr    13.3                                                            ______________________________________                                    

The average liquid residence time and temperature in the CSTR were 30minutes and 22° C., respectively. The oxygen feed rate to the CSTR was60 SCFH.

The reagents added to the centrifuged product from the CSTR were asfollows:

    ______________________________________                                                    Moles                                                             Reagent       Example 6 Example 7                                             ______________________________________                                        DBEDA         1.1       0.57                                                  Cu            0.97      0.32                                                  HBr           5.2       1.7                                                   ______________________________________                                    

The oxygen feed rate of the multi-zone reactor was 2.0 SCFH in bothexamples, the temperature thereof was 42° C. ±3° C. and the averageliquid residence time therein was 10 minutes. The polyphenylene oxideproducts had intrinsic viscosities of 0.61 dl./g. (Example 6) and 0.56dl./g. (Example 7).

EXAMPLE 8

The apparatus consisted of a 1-liter CSTR 5.5 inches in diameter,equipped with four vertical baffles (to pervent vortexing), a six-bladeagitator, an internal cooling coil and an oxygen sparging system.

A monomer solution was prepared by dissolving 36.8 grams of 50% aqueoussodium hydroxide in 200 ml. of methanol and adding this solution to asolution of 905 grams of 2,6-xylenol in 3790 ml. of toluene. A catalystsolution was also prepared, by dissolving 2.24 grams of manganese(II)chloride and 8.08 grams of benzoin oxime in 170 ml. of methanol.

A mixture of 980 ml. of monomer solution and 26 ml. of catalyst solutionwas charged to the reactor and oxygen was sparged into the mixture withstirring until steady state conditions were reached. Monomer andcatalyst solutions were then introduced at 32.7 and 0.86 ml. per minute,respectively, and oxygen was sparged in at 1.8 SCFH. The temperature ofthe reaction mixture was maintained at 30° C. The resulting reactionmixture contained 20% 2,6-xylenol and the following concentrations ofother ingredients:

    ______________________________________                                        Reagent            Moles                                                      ______________________________________                                        Manganese(II) chloride                                                                           1.8                                                        Benzoin oxime      3.6                                                        Sodium hydroxide   62                                                         ______________________________________                                    

After the reaction had been run continuously at steady state for sometime, an analysis of the polyphenylene oxide in the outlet stream showedan intrinsic viscosity of 0.10 dl./g. The feed and outlet streams werethen stopped and the remaining reactor contents were reacted inbatchwise fashion, with the same temperature and oxygen sparging rate.After 10 and 14 minutes of batch reaction, the polyphenylene oxideproducts (isolated by precipitation with methanol) had intrinsicviscosities of 0.39 and 0.76 dl./g., respectively.

EXAMPLE 9

The apparatus consisted of a CSTR similar to that of Example 8 buthaving a volume of 4.3 liters, in series with a multi-zone reactorsimilar to that of Example 1.

A monomer solution was prepared as described in Example 8 from 184 gramsof 50% aqueous sodium hydroxide solution, 750 ml. of methanol, 4520grams of 2,6-xylenol and 18.97 liters of toluene. A catalyst solutionwas also prepared from 10.3 grams of manganese(II) chloride, 37.0 gramsof benzoin oxime and 825 ml. of methanol.

The CSTR was charged with 4170 ml. of monomer solution and 130 ml. of ofcatalyst solution and brought to steady state at a temperature of 30° C.and an oxygen sparging rate of 3.3 SCFH. Addition of monomer andcatalyst solutions was then begun at feed rates of 139 and 4.3 ml. perminute, respectively, for an average liquid residence time of 30minutes. The reaction mixture contained 20% 2,6-xylenol and thefollowing proportions of other reagents:

    ______________________________________                                        Reagent            Moles                                                      ______________________________________                                        Manganese(II) chloride                                                                           2.0                                                        Benzoin oxime      4.0                                                        Sodium hydroxide   62                                                         ______________________________________                                    

The polymer in the effluent from the CSTR had an intrinsic viscosity of0.13 dl./g.

The CSTR outlet stream was introduced into the top of the multi-zonereactor and oxygen was introduced to the bottom thereof at 2.0 SCFH. Theaverage liquid residence time in the multi-zone reactor was 20 minutes,and the steady state temperature varied from 29° C. at the top to 40° C.at the bottom of the reactor. The polyphenylene oxide obtained wasisolated as previously described. It had an intrinsic viscosity of 0.60dl./g.

EXAMPLE 10

The procedure of Example 9 was repeated, except that the monomersolution also contained 10 moles of di-n-butylamine. The intrinsicviscosities of the polyphenylene oxides in the streams from the CSTR andthe multi-zone reactor were 0.15 and 0.35 dl./g., respectively.

What is claimed is:
 1. In a process for preparing polyphenylene oxidesby the catalytic reaction of oxygen with at least onemonohydroxyaromatic compound in solution in a solvent in which saidpolyphenylene oxide is also soluble, the improvement which comprisescarrying out said reaction in two stages, the first stage beingconducted continuously in at least one back-mixed reactor and the secondstage in at least one batch reactor or continuously in a reaction systemwith limited back-mixing.
 2. A process according to claim 1 wherein eachback-mixed reactor is a tank reactor and the second stage is conductedcontinuously in a limited back-mixing reactor.
 3. A process according toclaim 2 wherein the first stage takes place in one or twocontinuous-flow stirred tank reactors and the reaction temperature ineach of said tank reactors is in the range of about 10°-60° C.
 4. Aprocess according to claim 3 wherein at least about 65% conversion isachieved in the first tank reactor.
 5. A process according to claim 3wherein the second stage is effected in a continuous-flow tubularreactor.
 6. A process according to claim 5 wherein the continuous-flowtubular reactor contains multiple reaction zones, each of which isagitated.
 7. A process according to claim 6 wherein the continuous-flowtubular reactor contains at least five zones.
 8. A process according toclaim 7 wherein the reaction temperature in the continuous-flow tubularreactor is about 20°-60° C.
 9. A process according to claim 8 whereinthe monohydroxyaromatic compound is 2,6-xylenol.
 10. A process accordingto claim 7 wherein the reaction is conducted in an alkaline system inthe presence of a manganese complex catalyst.
 11. A process according toclaim 7 wherein the reaction is conducted in the presence of a catalystcomprising a combination of copper ions, halide ions and at least oneamine.
 12. A process according to claim 11 wherein water is removed fromthe reaction mixture after one or both tank reactors.
 13. A processaccording to claim 12 wherein only one tank reactor is used.
 14. Aprocess according to claim 13 wherein two tank reactors are used and theweight average molecular weight of the product is increased at leastfivefold in the second tank reactor.
 15. A process according to claim 14wherein the monohydroxyaromatic compound is 2,6-xylenol.
 16. A processaccording to claim 3 wherein the reaction is conducted in the presenceof a catalyst comprising copper ions, at least one secondary alkylenediamine and at least one tertiary monoamine.
 17. A process according toclaim 16 wherein the secondary alkylene diamine isN,N'-di-t-butylethylenediamine and the tertiary monoamine isdimethyl-n-butylamine.
 18. A process according to claim 17 wherein thecatalyst additionally contains at last one secondary monoamine.
 19. Aprocess according to claim 18 wherein the secondary alkylene diamine isN,N'-di-t-butylethylenediamine, the tertiary monoamine isdimethyl-n-butylamine and the secondary monoamine is dimethylamine ordi-n-butylamine.
 20. A process according to claim 19 wherein thereaction mixture also contains a phase transfer catalyst.
 21. A processaccording to claim 20 wherein the monohydroxyaromatic compound is2,6-xylenol.
 22. A process according to claim 10 wherein the catalystadditionally contains at least one secondary monoamine.
 23. A processaccording to claim 22 wherein the manganese complex is a benzoin oximecomplex.
 24. A process according to claim 3 wherein the reaction isconducted in the presence of a catalyst comprising a combination ofcopper ions, halide ions and at least one amine, and the non-gaseousconstituents are pre-mixed in an inert atmosphere to form a homogeneousmixture which is fed to the first stage.